Jacob Riglin

COMPUTATIONAL FLUID DYNAMICS AND STRUCTURAL FINITE ELEMENT ANALYSIS OF A MICRO HYDRO TURBINE

Performance characteristics of a micro hydro turbine are determined through the use of computation fluid dynamics (CFD) and finite element analysis (FEA). CFD is used to optimize a portable micro hydro turbine. The runner geometry is designed as a non-uniform Archimedean Spiral. The transient 3D turbulent flow simulation is conducted for various runner designs to determine power generation and the efficiency. The equations governing the fluid motion through the turbine are solved in a frame of reference change between time-steps. A multiphase flow model is employed to study the cavitation for various flow rates and rotation rates to determine the onset of the cavitation. It was determined that the onset of cavitation occurred between inlet flow rates of 0.0625 m 3 /s and 0.075 m 3 /s for the 1.5 pitch Archimedean spiral at a rotation rate of 250 RPM. When the rotation rate is increased to 500 RPM, vapor formation within the flow exists between a flow rate of 0.05 m 3 /s and 0.0625 m 3 /s. The occurrence of cavitation was predicted using Cavitation number, with the critical number being approximately -10,000. The presence of cavitation caused the efficiency to drop up to 10%. Basic structural analysis of the Archimedean blade yielded a maximum von Mises stress of 143.67 MPa at flow rate of 0.1 m 3 /s and a rotation rate of 1000 RPM. From the von Mises stress obtained, aluminum alloy is the best material to be used based on the importance of material strength and weight.

Numerical analysis of a shrouded micro-hydrokinetic turbine unit

ABSTRACT Computational fluid dynamics simulations were conducted for two diffuser designs that were added to a pre-existing horizontal axis hydro-kinetic turbine design. The two diffuser designs investigated in the present study had the area ratio values of 1.36 and 2.01. Each design used a short axial length to satisfy system portability constraints. The turbine-diffuser systems steady-state performance characteristics were assessed numerically. A structured, hexahedral mesh was employed to discretize the equations governing the fluid motion. Turbulent flow structures were captured through the implementation of the k-ω Shear Stress Transport (SST) model. A 39.5% and 55.8% increase in output mechanical power was observed versus the un-augmented turbine performance. As the area ratio increases from 1.36 to 2.01, the total thrust experienced by the unit nearly doubles.

Computational Study of Multiple Hydrokinetic Turbines: The Effect of Wake

Computational Fluid Dynamics (CFD) simulations have been conducted to investigate the performance of a predetermined propeller-based hydrokinetic turbine design in staggered and non-staggered placements for river applications. Actual turbine models were used instead of low fidelity actuator line or actuator disks for CFD simulations to achieve more reliable results. The k-ω Shear Stress Transport (SST) turbulence model was employed to resolve wall effects on turbine surface and to determine wake interactions behind the turbines. The wake interaction behind the upstream turbine causes significant drop on downstream turbine performance within non-staggered configuration. The upstream turbines in both staggered and non-staggered placement offers the same relative power of 0.96, while the relative power for downstream turbine is 0.98 for staggered installment and 0.16 for inline placement.Copyright

Diffuser Optimization for a Micro-Hydrokinetic Turbine

Small, hydrokinetic systems generating between 0.5 and 10 kW of power are potentially capable of portable power generation. A propeller turbine 18 inches in diameter is paired with a flanged diffuser and numerically simulated as a potential portable hydrokinetic system. The diffuser augmented hydrokinetic turbine (DAHkT) is investigated with a response surface optimization method, where geometric parameters of the system are systematically varied to determine their effects on the system power generation and thrust. The simulations are determined using a central composite design of experiments to minimize the number of simulations required to fit a second-order regression to the results. Potential optimum designs are determined from the regression model, further verified with simulations, and characterized for their entire operating range.Copyright

Design and Characteristics of the Micro-Hydrokinetic Turbine System

Small, hydrokinetic systems generating between 0.5 and 10 kW of power allow for the potential of portable power generation. An optimized propeller turbine approximately 0.6826 m in diameter and a diffuser with an area ratio of 1.31 were used to produce a prototype for preliminary testing. The optimized diffuser augmented hydrokinetic turbine was investigated numerically to predict power and thrust curves for comparison during experimental testing. A gear box with a 10:1 gear ratio was selected for converting torque to angular velocity. A DC permanent magnet generator was selected for mechanical-electrical power conversion. At the ideal generator operating conditions consisting of a shaft rotation rate of 1150 RPM, a voltage of 48 V, and current of approximately 8 A, 375 W of power may be generated at a river flow speed of 1.5 m/s. Numerical predictions coupled with component efficiencies yield a system efficiency of approximately 0.61 before DC/DC conversion and 0.52 after DC/DC conversion.Copyright